Routing in Mobile Ad hoc NETworks MANET

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Routing in Mobile Ad hoc NETworks (MANET)

• Manish Agarwal

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Outline

• MANET overview
• Connectivity Routing in MANET
• Routing with special constrains
• Open issues and future directions

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Point-to-multipoint networks

• Cellular networks
• IEEE 802.11

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Mobile Ad Hoc Networks

• Formed by wireless autonomous hosts
• Without (necessarily) using a pre-existing
  infrastructure
• Routes between hosts may potentially contain
  multiple hops
• Host mobility cause route changes
• Shared wireless channel

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Why Ad Hoc Networks ?

• Ease of deployment
• Speed of deployment
• Decreased dependence on infrastructure
• User flexibility

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Application areas

• Military environments
• Battle field sensors, soldiers, vehicles
• Emergency operations
• search-and-rescue
• policing and fire fighting
• Civilian environments
• conference halls
• sports stadiums, Library, etc.
• Personal area networking
• laptop, PDA, cell phone, ear phone, wrist watch

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Challenges

• Lack of centralized entity
• Shared unreliable wireless medium
• Low bandwidth
• Hidden/exposure node effect
• Ease of snooping on wireless transmissions
• Mobility-induced route changes/packet losses
• Battery constraints
• Asymmetric Capabilities
• transmission ranges
• battery life
• processing capacity
• Speed/pattern of movement

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Outline

• MANET overview
• Connectivity Routing in MANET
• Routing with special constrains
• Open issues and future directions

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Why is Routing in MANET different ?

• Host mobility
• link failure/repair due to mobility may have
  different characteristics than those due to other
  causes
• Rate of link failure/repair may be high when
  nodes move fast
• Distributed Environment
• New performance criteria may be used
• route stability despite mobility
• Packet Delivery ratio
• Routing Overhead

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Ad hoc Routing Protocols

• Proactive protocols (DSDV)
• Traditional link-state and distance-vector
  routing protocols
• Continuously update the reachability
  information at all the network nodes
• Lower route request latency and higher overhead
• Reactive protocols (AODV, DSR)
• Maintain routes only if needed
• Flooding of control message
• higher latency and lower overhead
• Source routing/hop-by-hop routing
• Hybrid protocols (OLSR, ZRP, CEDAR)
• Constrained link state maintenance
• Route established on-demand
• Which approach achieves a better trade-off
  depends on the traffic and mobility patterns

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Dynamic Source Routing (DSR)

• On-demand routing
• Source routing Data transmitting method with
  path info. In the data packet explicitly
• Nodes contain tables of full paths to other nodes
• Messages Route Request (RREQ), Route Reply
  (RREP), Route Error (RERR)

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Routing Mechanism

• Route Discovery
• To find a route to destination.
• When ?
• Route maintenance
• Adapt to the changes in network topology. For
  example node moving

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Routing Details - route discovery
C

• Route Cache

B
A
E
D
Route cache in node A
Dest. Route A X B direct C B D B E BD
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Route Requests in DSR
Y
Broadcast transmission
Z
S
E
F
B
C
M
L
J
A
G
H
D
K
I
N
Represents a node that has received RREQ
Represents transmission of RREQ
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Route Requests in DSR
Y
Z
S
E
F
B
C
M
L
J
A
G
H
D
K
I
N
assumes symmetric (bi-directional) links
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Route Requests in DSR
Y
Z
S
E
F
B
C
M
L
J
A
G
H
D
K
I
N

• Node C receives RREQ from G and H, but does not
  forward
• it again, because node C has already forwarded
  RREQ once

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Routing Details - route discovery

• Route Request

Route record List of nodes traversed by RREQ
Process 1. Each RREQ packet contains a route
record 2. If this host is in the route record,
discard this request 3. If target this host or
I have path for target in cache, send Route
Reply packet 4. Otherwise, add this host to
route record and rebroadcast the route
request.
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Routing Details - route discovery

• Route Reply Return

Return path is from 1. This hosts route cache
or target node 2. Reverse the route record and
send the RREP to the source
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Route Reply in DSR
Y
Z
S
E
F
B
C
M
L
J
A
G
H
D
K
I
N
Represents links on path taken by RREP
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Data Delivery in DSR
Y
DATA
Z
S
E
F
B
C
M
L
J
A
G
H
D
K
I
N
Route is included in packet header.
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Link Failure Detection

• Hello messages Neighboring nodes periodically
  exchange hello message
• Absence of hello message is used as an indication
  of link failure
• Alternatively, failure to receive several
  MAC-level acknowledgement may be used as an
  indication of link failure

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Link Failure Reporting

• A neighbor of node X is considered active for a
  routing table entry if the neighbor sent a packet
  within active_route_timeout interval which was
  forwarded using that entry
• When the next hop link in a routing table entry
  breaks, all active neighbors are informed
• Link failures are propagated by means of Route
  Error messages

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Route Error

• When node X is unable to forward packet (from
  node S to node D) on link (X,Y), it generates a
  RERR message and sends it to node S
• When node S receives the RERR, it initiates a new
  route discovery for D

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Location-Aided Routing (LAR)

• Exploits location information to limit scope of
  route request flood
• Location information may be obtained using GPS
• Expected Zone is a region that is expected to
  hold the current location of the destination
• Route requests limited to a Request Zone that
  contains the Expected Zone and location of the
  sender node

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Expected Zone in LAR

• Based on potentially old location information,
  and knowledge of the destinations speed
• X last known location of node D, at time t0
• Y location of node D at current time t1,
  unknown to node S
• r (t1 - t0) estimate of Ds speed

X
r
Y
Expected Zone
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LAR

• Request zone explicitly specified in the route
  request
• Only nodes within the request zone forward route
  requests
• Each node must know its physical location to
  determine whether it is within the request zone

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LAR Variations

• Node X forwards a route request from Y if node X
  is deemed to be closer to the expected zone than
  Y
• Adaptive Request Zone Each node may modify the
  request zone included in the forwarded request
  using more recent/accurate information,

B
S
Request zone adapted by B
Request zone defined by sender S
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Location Aided Routing (LAR)

• Advantages
• reduces the scope of route request flood
• reduces overhead of route discovery
• Disadvantages
• Nodes need to know their physical locations
• Does not take into account possible existence of
  obstructions for radio transmissions

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Hybrid Protocols

• Proactive protocol which pro-actively updates
  network state and maintains route regardless of
  whether any data traffic exists or not
• Reactive protocol which only determines route to
  a destination if there is some data to be sent to
  the destination

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Hierarchical ad hoc network
A two tier Ad hoc Network
Tier 2 network
Cluster
cluster head
Tier 1 network
Tier 1 network
Tier 1 network
Tier 1 network
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Core-Extraction Distributed Ad Hoc Routing (CEDAR)

• Core extraction
• Establishment maintenance of a routing
  infrastructure called core
• Finding core (Minimum Connected Dominating Sets)
  is NP-complete
• Each node picks one core node as its dominator
• Dominator node is chosen based on the degree of
  the outgoing link
• Periodical Link state propagation
• propagation of the link-state of stable
  high-bandwidth links in the core
• Route computation
• route computation at the core nodes using all
  pair shortest path algorithm
• Route from S to D may or may not include core
  nodes

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Route Discovery in CEDAR

• Node S informs its dominator core node A
• Node A finds a route in the core network to the
  core node B which is the dominator for
  destination D
• Core nodes on the above route between A and B
  then build a route from S to D using locally
  available link state information
• Route from S to D may or may not include core
  nodes

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CEDAR

• Advantages
• Route discovery/maintenance duties limited to a
  small number of core nodes
• Link state propagation a function of link
  stability/quality
• Disadvantages
• Core nodes have to handle additional traffic,
  associated with route discovery and maintenance
• Hard to converge under high mobility

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Outline

• MANET overview
• Connectivity Routing in MANET
• Routing with special constrains
• Power
• Security
• QoS
• Open issues and future directions

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Power-Aware Routing criteria

• Define optimization criteria as a function of
  energy consumption. Examples
• Minimize energy consumed per packet
• Minimize time to network partition due to energy
  depletion
• Maximize duration before a node fails due to
  energy depletion

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Power-Aware Routing approach

• Assign a weight to each link
• Weight of a link may be a function of
• energy consumed when transmitting a packet on
  that link
• residual energy level
• Prefer a route with the smallest aggregate weight

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Challenges in ad hoc QoS routing

• Admission control
• Make admission decision with time-varying link
  capacity
• How to measure end-to-end delay in a
  unsynchronized network?
• Resource reservation
• Guarantee the availability of the reserved
  bandwidth over shared medium (need support from
  MAC)
• QoS failure detection and recovery
• Delay violation detection
• Detect route break by neighbor lost is too slow!
• Any thing better than re-discovery?
• Low control overhead
• Route establish/maintenance/tear down

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Security Issues in Mobile Ad Hoc Networks Whats
New ?

• Ad hoc network based on peer cooperation
• Can you trust your peer?
• Wireless medium is easy to snoop on
• Trace the path of active routes
• Easier for intruders to insert themselves into
  the network
• Everybody is a router
• inject erroneous routing information
• divert network traffic, or
• make routing inefficient
• Due to ad hoc connectivity and mobility, it is
  hard to guarantee access to any particular node
  (for instance, to obtain a secret key)

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Secure Routing

• Use of digital signatures to protect routing
  information and data both
• Such schemes need a Certification Authority to
  manage the private-public keys
• Distributing the CA function over multiple nodes
• single authority may not be reachable from all
  nodes at all times

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Intrusion Detection

• Detection of abnormal routing table updates
• Uses training data to determine characteristics
  of normal routing table updates
• Efficacy of this approach is not evaluated, and
  is debatable
• Similar abnormal behavior may be detected at
  other protocol layers
• For instance, at the MAC layer, normal behavior
  may be characterized for access patterns by
  various hosts

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Open Problems

• Address assignment problem
• Stationary or auto-configuration?
• Improving interaction between protocol layers
• Some routing protocol need feed back from MAC to
  detect link status
• Position information from higher layer
• Integration with Internet
• Existing ad hoc routing with infrastructure nodes
• Different network perspectives

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The End.

• Thank you!